CN114014602A - Self-repairing cement-based material and preparation method and test method thereof - Google Patents
Self-repairing cement-based material and preparation method and test method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
- C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/38—Concrete; Lime; Mortar; Gypsum; Bricks; Ceramics; Glass
- G01N33/383—Concrete or cement
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
- C04B2111/34—Non-shrinking or non-cracking materials
- C04B2111/343—Crack resistant materials
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
- C04B2111/90—Electrical properties
- C04B2111/94—Electrically conducting materials
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2201/00—Mortars, concrete or artificial stone characterised by specific physical values
- C04B2201/05—Materials having an early high strength, e.g. allowing fast demoulding or formless casting
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2201/00—Mortars, concrete or artificial stone characterised by specific physical values
- C04B2201/50—Mortars, concrete or artificial stone characterised by specific physical values for the mechanical strength
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Ceramic Engineering (AREA)
- General Physics & Mathematics (AREA)
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- Pathology (AREA)
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- Physics & Mathematics (AREA)
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- General Health & Medical Sciences (AREA)
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- Inorganic Chemistry (AREA)
- Materials Engineering (AREA)
- Electrochemistry (AREA)
- Organic Chemistry (AREA)
- Food Science & Technology (AREA)
- Medicinal Chemistry (AREA)
- Curing Cements, Concrete, And Artificial Stone (AREA)
Abstract
A self-repairing cement-based material, a preparation method and a test method thereof belong to the technical field of crack self-repairing agents. The cement-based material is prepared by adding 15-25g of microcapsules and 0.75-1.25g of graphene oxide into 1000g of concrete mortar according to the weight ratio. The preparation method comprises the following steps: preparing a core material, a wall material solution and microcapsules, carrying out microcapsule detection, preparing graphene oxide, and preparing the self-repairing cement-based material. The test method comprises the following steps: taking a test block, performing pressure preloading and soaking, and observing the micro-capsule microscopic form, crack repair and component composition of the test block; arranging electrodes on the test block, and applying a direct current power supply to the electrodes; and verifying whether the product is qualified. The invention solves the problems of the long-term service characteristics and the grounding resistance of the foundation faced by the power transmission and transformation project in the special environment of northwest region. The concrete has improved integral bearing capacity, rigidity, grounding capacity, crack resistance and service performance, and saves cost and material.
Description
Technical Field
The invention relates to a self-repairing cement-based material, a preparation method and a test method thereof, belonging to the technical field of crack self-repairing agents.
Background
With the rapid development of electric power facilities in China, a large number of power transmission and transformation projects pass through northwest areas, and the foundation of a power transmission tower is affected by complex environments such as saline soil, collapsible loess, extreme temperature and rainfall conditions, so that the foundation is easily damaged by corrosion, frost heaving, thawing sinking, cracks and the like. Meanwhile, foundation construction belongs to hidden engineering, once microcracks appear, the repairing is difficult, through cracks can be caused, and the durability and the stability of the foundation of the power transmission and transformation engineering are seriously influenced. In addition, the grounding grid is an important measure for ensuring the safe and reliable operation of an electric power system and the safety of personnel and equipment, the grounding resistance of the grounding grid is one of the main technical parameters of the grounding grid, the resistivity of common concrete is as high as 104-109 omega-m, and the most important measure is to reduce the grounding resistance in order to ensure the normal work of the power connection grid. Therefore, the complex and variable meteorological geological environment and power grid grounding engineering design requirements will put higher demands on concrete materials, and also face many new challenges.
At present, the pile foundation of the power transmission tower is constructed by adopting cast-in-place piles, the power transmission and transformation project is often constructed in the field or in a steep terrain area, and the foundation construction quality is easily influenced by the field environment and the construction conditions. Secondly, the foundation is in complex environments such as drought, low temperature, sand blown by the wind and the like, the crack resistance and the corrosion resistance of the foundation are poor, once the crack is generated on the foundation, the crack growth is accelerated under the influence of water and low temperature in the soil body, and the concrete foundation is damaged. Meanwhile, the power transmission tower foundation belongs to hidden engineering, cracks are not easy to perceive in the foundation or on the surface of the foundation, the follow-up repairing difficulty is high, and related problems need to be solved urgently.
Based on the bionics theory, repair materials are buried in concrete in advance, when a concrete structure is damaged, the repair materials are triggered by different trigger mechanisms (such as temperature, alkalinity or cracks) to repair the damaged area, and therefore long-term service of the concrete structure is prolonged, and durability is improved.
The microcapsules researched at present are urea-formaldehyde resin/epoxy microcapsules and phenol-formaldehyde resin/dicyclopentadiene microcapsules, the bonding property and the expansibility of a capsule core material are relatively weak, and the structural strength of a capsule wall is low, so that the engineering application of the microcapsule in a cement-based material system is limited. The preparation method mainly comprises a physical method, a chemical method, a physicochemical method and the like. Numerous scholars respectively develop tests and numerical simulation in the fields of petrochemical engineering, highway engineering, bridge engineering, high polymer materials, coatings and the like to obtain certain scientific research achievements, relatively few researches on crack resistance of concrete foundations of power transmission and transformation engineering based on complex geological meteorological conditions in the northwest region exist, and the corrosion cracking phenomenon is prominent because the foundations are influenced by external environments. Meanwhile, the particularity of the power transmission and transformation project and the requirement of the foundation ground resistance put higher requirements on the composition of the concrete material. The most commonly used conductive media today include: graphite, carbon fiber, steel slag, carbon black and the like. The graphene has good conductivity and an oversized specific surface area, the conductivity of the cement-based material can be obviously improved by the high-doping amount of graphene, but the high-doping amount of graphene is high in manufacturing cost and can cause the mechanical property of the material to be reduced, so that the popularization and the use of the graphene are severely restricted. The conductive performance of the cement mortar can be enhanced by the metal fibers, but the conductive network and the construction mixing problem are directly influenced by the amount of the metal fibers. Therefore, in consideration of long-term service performance, stability and foundation grounding capability of power transmission and transformation engineering, microcapsules and conductive materials with strong cohesiveness and good expansibility are urgently needed to solve the engineering problem faced by the power transmission tower foundation in northwest regions.
Disclosure of Invention
In order to solve the problems in the background art, the invention provides a self-repairing cement-based material, a preparation method and a test method thereof.
The invention adopts the following technical scheme: the self-repairing cement-based material is prepared by adding 15-25g of microcapsules and 0.75-1.25g of graphene oxide into 1000g of concrete mortar; the concrete mortar comprises 23% of cement, 67% of sand and 10% of water by weight.
A method for preparing a self-healing cement-based material, the method comprising the steps of:
s1: preparing a core material;
s2: preparing a wall material solution;
s3: preparing microcapsules;
s4: carrying out integrity detection on the outer wall of the microcapsule;
s5: preparing graphene oxide;
s6: and preparing the self-repairing cement-based material.
A method of testing a self-healing cement-based material, the method comprising the steps of:
the method comprises the following steps: taking the self-repairing cement-based material test block obtained in the step S605, and preloading the test block for not less than 3 min;
step two: soaking the test block of the self-repairing cement-based material obtained in the step S605 in water for 30 days;
step three: observing the micro morphology, crack repair and component composition of the microcapsules in the test block obtained in the step two;
step four: uniformly arranging four stainless steel electrodes on the test block obtained in the step two;
step five: applying a direct current power supply to the stainless steel electrode in the step four to obtain voltage and current in a line;
step six: and verifying the strength increase rate and the self-repairing rate of the test block, so that the strength of the test block is improved by more than 10% compared with that of common concrete, and the self-repairing rate of the test block reaches more than 90%, indicating that the test block is qualified, otherwise, indicating that the test block is unqualified.
Compared with the prior art, the invention has the beneficial effects that:
1. the method efficiently and conveniently solves the problems of long-term service characteristics and grounding resistance of the foundation faced by the power transmission and transformation project in the special environment of the northwest region, is not limited by extremely variable meteorological and geological conditions and the like, and avoids the problems of poor concrete quality, high repairing and reinforcing difficulty, low long-term service performance and the like caused by large-volume integral pouring of concrete in the special soil environment such as saline soil and the like.
2. The self-repairing material is used for self-repairing of a composite cement-based material, the graphene oxide material is doped externally to improve the conductivity of the material, the integral bearing capacity, rigidity, grounding capacity, crack resistance and service performance of concrete are greatly improved, and meanwhile, the cost and the use of the material are saved.
3. The invention meets the requirements of long-term high-load operation of the field power transmission tower foundation on ecological balance and environmental friendliness, fully utilizes the action of the microcapsules in the concrete to realize self-repair, avoids introducing a large amount of chemical grouting materials, and has important guiding significance for selecting high-efficiency self-repairing agents for the disease control of the power transmission tower foundation. Meanwhile, the graphene oxide has good grounding capacity and pressure-sensitive performance, so that the safety of the power transmission iron tower can be directly improved, and series natural damage caused by electric leakage or high-altitude work is reduced.
4. The microcapsules and the graphene oxide are doped into the concrete mortar to serve as the grouting material for the foundation pile body of the power transmission tower, so that active self-repairing can be realized when micro cracks or cracks appear in the power transmission tower foundation, and the expansibility damage of the internal cracks can be prevented.
Drawings
FIG. 1 is a photograph of a microcapsule prepared according to the present invention;
FIG. 2 is a photograph of a crack repaired by a graphene oxide-microcapsule embedded cement test block according to the present invention;
FIG. 3 is a cross-sectional photograph of a graphene oxide-microcapsule-embedded cement test block according to the present invention
FIG. 4 is a composition of graphene oxide-microcapsule cement-based material of the present invention;
FIG. 5 is a flow chart of the preparation of the present invention;
Detailed Description
The technical solutions in the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the invention, rather than all embodiments, and all other embodiments obtained by those skilled in the art without any creative work based on the embodiments of the present invention belong to the protection scope of the present invention.
The self-repairing cement-based material is prepared by adding 15-25g of microcapsules and 0.75-1.25g of graphene oxide into 1000g of concrete mortar; the graphene oxide and the microcapsule are doped into the concrete mortar together to serve as the grouting material for the foundation pile body of the power transmission tower, and based on an orthogonal test, the optimal recommended doping amount of the microcapsule in the optimized material is 2% and the optimal doping amount of the graphene oxide is 0.1%. The concrete mortar comprises 23% of cement, 67% of sand and 10% of water by weight, and the calculated water cement ratio is 0.45.
The microcapsule comprises a core material and a wall material; the wall material is wrapped on the outer side of the core material and consists of 10% of ethyl cellulose, 18% of ethanol and 72% of xylene according to the weight ratio; the core material consists of 10% of bentonite, 25% of sodium silicate, 30% of microcrystalline cellulose, 2% of methyl cellulose, 4% of tween 80 and 29% of distilled water.
The graphene oxide is prepared by adding 10g of graphene oxide nano-particles into 1000g of water according to the weight ratio.
A method for preparing a self-healing cement-based material, the method comprising the steps of:
s1: preparing a core material;
s101: screening sodium silicate, methylcellulose and microcrystalline cellulose by using a 0.5mm square-hole sieve to ensure that the powder of the sodium silicate, the methylcellulose and the microcrystalline cellulose have uniform particle size and no larger particles are mixed;
s102: pouring Tween 80 into distilled water, and stirring until the Tween 80 and the distilled water are completely mixed;
s103: pouring bentonite, sodium silicate obtained in the step S101, methylcellulose and microcrystalline cellulose into a mixed solution of Tween 80 obtained in the step S102 and distilled water to obtain an off-white muddy substance;
s104: preparing core material particles: putting the yellowish pasty substance obtained in the step S103 into a manual granulator, stirring and extruding, extruding by a disc with a small hole with the diameter of one millimeter, cutting by a cutter to form yellowish wet granules, and drying the granules in a drying oven for 12 hours to obtain yellowish core material granules.
S2: preparing a wall material solution;
mixing all wall material raw materials, and uniformly stirring to prepare a transparent colloidal solution;
s3: preparing microcapsules;
s301: uniformly spraying the wall material solution obtained in the step S2 on the core material particles prepared in the step S104 by using a watering can;
s302: drying the core material particles obtained in the step S301 for 4 hours by using a drying box;
s303: in order to ensure that the wall material completely wraps the core material, the process from S301 to S302 needs to be repeated twice to ensure that the capsule wall of each microcapsule particle is completely sealed;
s304: and screening the obtained dark yellow particles by using square-hole sieves with the particle sizes of 0.5mm and 2.0mm respectively to obtain the microcapsule with the particle size of 0.5-2.0 mm.
S4: carrying out integrity detection on the outer wall of the microcapsule;
s401: soaking the microcapsule obtained in the step S3 in distilled water for not less than 24 hours;
s402: observing the integrity of the microcapsules, wherein if the dissolution rate of the particles is less than 15%, the integrity of the outer walls of the microcapsules is good, namely the self-repairing cement-based material is prepared; on the contrary, the integrity of the outer wall of the microcapsule is poor, i.e. the microcapsule needs to be prepared again.
S5: preparing graphene oxide;
adding the graphene oxide nano particles into water, uniformly stirring, placing the solution into an ultrasonic instrument, controlling the temperature to be 20 degrees, controlling the power of the ultrasonic instrument to be 350 watts, controlling the reaction time to be 2 hours, immediately placing the formed uniform graphene oxide solution into cement mortar to mix with microcapsules, mixing the solution and the microcapsules together during foundation pouring, and pouring and forming.
S6: and preparing the self-repairing cement-based material.
S601: uniformly stirring cement, gravel and water in a planetary stirrer, and adding graphene oxide and microcapsules according to the optimal mixing ratio while stirring to prepare a self-repairing cement-based material;
s602: pouring the material obtained in the step S601 into a test mold;
s603: vibrating the test mold on a vibrating table for 50-70 s;
s604: maintaining the test mold for 24h, and then removing the mold;
s605: and (4) placing the demolded material in a standard curing room for curing for 28 days to obtain a self-repairing cement-based material test block, and finally moving to field application.
A method of testing a self-healing cement-based material, the method comprising the steps of:
the method comprises the following steps: taking the self-repairing cement-based material test block obtained in the step S605, and preloading the test block for not less than 3min, wherein the preloading pressure is 70% of the 28d ultimate compressive strength of the test block;
step two: soaking the test block of the self-repairing cement-based material obtained in the step S605 in water for 30 days, and observing the crack repairing effect;
step three: observing the micro-morphology, crack repair and component composition of the microcapsules in the test block obtained in the step two through an optical microscope and X-ray diffraction;
micro-capsule morphology: the optical microscope finds that the microcapsule is approximately spherical, the shell is completely wrapped, the surface of the microcapsule is completely covered by the wall material, the wall material structure is compact, the outer wall is very smooth, the integrity of the wrapping of the outer wall of the microcapsule is basically guaranteed, and the core material can be completely protected under the condition that the outer wall is not broken. After the microcapsule is continuously amplified, the surface of the microcapsule is uneven, the edge of the microcapsule is irregular, the microcapsule can be firmly bonded with surrounding materials after being doped into concrete, once a crack section passes through the microcapsule, the microcapsule can be smoothly broken by pulling the concrete at two sides, the core material is released, and the filling and repairing work of the crack is completed.
And (3) component analysis: the material is found to mainly comprise albite, anorthite, quartz, portlandite, brushite, ettringite and calcite by an X-ray diffraction method, wherein the albite and the anorthite account for 73 percent of the composition of the phase, and the quartz accounts for 19 percent. Compared with a common test piece, the content of the quartz, albite and anorthite in the material added with the microcapsules is respectively increased by 2 percent, 22 percent and 23 percent, and the relative content of other substances is reduced to a certain extent. This phenomenon illustrates that the core material is released and reacts after the microcapsule cracks, producing more calcium silicate and silicon dioxide, constituting the main components of the cement-based material, and also demonstrates that the capsule core material used meets the need for repairing cracks.
Step four: uniformly arranging four stainless steel electrodes on the test block obtained in the step two according to the distance of 20 mm;
step five: applying a direct current power supply to the stainless steel electrode in the step four, and acquiring voltage and current in the line by using a current meter and a voltage meter;
conductivity: the excellent dispersibility and hydrophilicity of the graphene oxide in water accelerate the release and hydration reaction of the core material in the microcapsule, and the calcium ions in the material are obviously improved by comparing the composition of the graphene oxide before and after the graphene oxide is added, so that more crystals are generated, and the mineral deposits fill up the microcracks. Meanwhile, anorthite (55%) in the test piece has small dielectric constant and high specific strength, reduces the resistivity in a cement base, and meets the requirement of a low-resistivity grounding network in a power transmission network.
Microscopic morphology of graphene: the color of the interior of the test piece is darker, the interior of the test piece is uniformly distributed, and the agglomeration phenomenon does not occur. Meanwhile, the internal structure of the test piece is more compact, the mechanism that the graphene oxide enhances the strength of the test piece is met, the graphene promotes the hydration reaction, and the hydration products are connected to form the enhancing effect.
Self-repairability: the compression strength of the test block can reach 3.9MPa, the strength restoration rate can reach more than 92%, the final setting time of the cement mortar is within 1h, and the influence on the fluidity and the setting time of the cement mortar is small.
Step six: and verifying the strength increase rate and the self-repairing rate of the test block, so that the strength of the test block is improved by more than 10% compared with that of common concrete, and the self-repairing rate of the test block reaches more than 90%, indicating that the test block is qualified, otherwise, indicating that the test block is unqualified.
The graphene oxide is doped during foundation pouring, so that the conductivity of the foundation is enhanced, the influence of extreme weather, special soil environment, construction conditions and the like is avoided under the condition of the optimal proportion of the graphene oxide to the microcapsules, the construction quality of coagulation is guaranteed, the grounding capacity, frost resistance and crack resistance of the power transmission tower foundation are enhanced, and the durability, the bearing capacity and the service performance of a pile body are greatly improved.
The invention has the advantages of strong applicability, low cost, convenient control of the synthesis process, easy uniform dispersion in cement-based materials and the like.
The self-repairing graphene oxide material is used for self-repairing of a composite cement-based material, and the externally doped graphene oxide material is used for improving the conductivity of the material. The construction method effectively solves the problems of complicated and changeable construction and technology in the process of constructing the power transmission tower pile foundation in the special environment of the northwest region, greatly improves the integral bearing capacity, rigidity, grounding capacity, crack resistance and service performance of concrete, and saves cost and material.
The invention meets the foundation construction requirement in power transmission and transformation engineering, wherein the wall material of the microcapsule has a protection effect on the core material in the microcapsule, and the wall material has mechanical triggering performance, so that when a micro crack is generated on the foundation of a power transmission tower, the wall material of the microcapsule at or near the crack can be automatically pressed and broken, the surrounding water permeates into the crack through capillary action and reacts with the core material to generate Si (OH) with gel property4After curing, the gap is bonded, and the adhesive has certain bonding strength. The bentonite in the core material expands after absorbing water to fill cracks, so that external corrosive substances cannot enter the interior of the foundation through the cracks. Finally, crackThe grains are completely bonded together and the base stiffness and permeability of the material are restored. After the graphene oxide is added, calcium ions in the material are obviously improved, more crystals are generated, and mineral deposition is performed to fill up micro cracks. Meanwhile, anorthite (55%) in the test piece has small dielectric constant and high specific strength, reduces the resistivity in a cement base, and meets the requirement of a low-resistivity grounding network in a power transmission network.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.
Claims (9)
1. A self-repairing cement-based material is characterized in that: adding 15-25g of microcapsules and 0.75-1.25g of graphene oxide into 1000g of concrete mortar according to the weight ratio; the concrete mortar comprises 23% of cement, 67% of sand and 10% of water by weight.
2. The self-healing cement-based material of claim 1, wherein: the microcapsule comprises a core material and a wall material; the wall material is wrapped on the outer side of the core material and consists of 10% of ethyl cellulose, 18% of ethanol and 72% of xylene according to the weight ratio; the core material consists of 10% of bentonite, 25% of sodium silicate, 30% of microcrystalline cellulose, 2% of methyl cellulose, 4% of tween 80 and 29% of distilled water.
3. The self-healing cement-based material of claim 1 or 2, wherein: the graphene oxide is prepared by adding 10g of graphene oxide nano-particles into 1000g of water according to the weight ratio.
4. A method of making a self-healing cementitious material according to claim 2 or 3, characterised in that: the method comprises the following steps:
s1: preparing a core material;
s2: preparing a wall material solution;
s3: preparing microcapsules;
s4: carrying out integrity detection on the outer wall of the microcapsule;
s5: preparing graphene oxide;
s6: and preparing the self-repairing cement-based material.
5. The method for preparing the self-repairing cement-based material of claim 4, wherein the method comprises the following steps: the S1 includes the following steps:
s101: screening sodium silicate, methylcellulose and microcrystalline cellulose;
s102: pouring Tween 80 into distilled water, and stirring until the Tween 80 and the distilled water are completely mixed;
s103: pouring bentonite, sodium silicate obtained in the step S101, methylcellulose and microcrystalline cellulose into a mixed solution of Tween 80 obtained in the step S102 and distilled water to obtain an off-white muddy substance;
s104: core material particles are prepared.
6. The method for preparing the self-repairing cement-based material of claim 5, wherein the method comprises the following steps: the S3 includes the following steps:
s301: spraying the wall material solution obtained in the step S2 on the core material particles prepared in the step S104;
s302: drying the core material particles obtained in the step S301 for 4 hours;
s303: repeating the processes of S301-S302 twice;
s304: screening to obtain the microcapsule with the particle size of 0.5-2.0 mm.
7. The method for preparing the self-repairing cement-based material of claim 5, wherein the method comprises the following steps: the S4 includes the following steps:
s401: soaking the microcapsule obtained in the step S3 in distilled water for not less than 24 hours;
s402: observing the integrity of the microcapsule, wherein if the dissolution rate of the particles is less than 15%, the integrity of the outer wall of the microcapsule is good; on the contrary, the integrity of the outer wall of the microcapsule is poor, i.e. the microcapsule needs to be prepared again.
8. The method for preparing the self-repairing cement-based material of claim 5, wherein the method comprises the following steps: the S6 includes the following steps:
s601: uniformly stirring cement, gravel and water, and adding graphene oxide and microcapsules while stirring;
s602: pouring the material obtained in the step S601 into a test mold;
s603: vibrating the test mold for 50-70 s;
s604: maintaining the test mold for 24h, and then removing the mold;
s605: and maintaining the demolded material for 28 days to obtain the self-repairing cement-based material test block.
9. The method for testing the self-healing cement-based material of claim 8, wherein: the method comprises the following steps:
the method comprises the following steps: taking the self-repairing cement-based material test block obtained in the step S605, and preloading the test block for not less than 3 min;
step two: soaking the test block of the self-repairing cement-based material obtained in the step S605 in water for 30 days;
step three: observing the micro morphology, crack repair and component composition of the microcapsules in the test block obtained in the step two;
step four: uniformly arranging four stainless steel electrodes on the test block obtained in the step two;
step five: applying a direct current power supply to the stainless steel electrode in the step four to obtain voltage and current in a line;
step six: and verifying the strength increase rate and the self-repairing rate of the test block, so that the strength of the test block is improved by more than 10% compared with that of common concrete, and the self-repairing rate of the test block reaches more than 90%, indicating that the test block is qualified, otherwise, indicating that the test block is unqualified.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114477838A (en) * | 2022-02-21 | 2022-05-13 | 四川省建筑科学研究院有限公司 | Crack self-repairing material applied to concrete |
| CN115684279A (en) * | 2022-10-31 | 2023-02-03 | 江苏科技大学 | Quantitative test device and method for crack self-repairing effect of cement-based material |
| CN116573913A (en) * | 2023-05-08 | 2023-08-11 | 浙江台州利伟节能建材有限公司 | Light plastering gypsum mortar and preparation method thereof |
| CN117362002A (en) * | 2023-12-04 | 2024-01-09 | 山东理工大学 | High-temperature phase-change heat-storage ceramic tile with solid waste as raw material and preparation method thereof |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2015074343A1 (en) * | 2013-11-25 | 2015-05-28 | 深圳大学 | Microencapsulation method for concrete water-based repair agent |
| CN104944833A (en) * | 2015-03-31 | 2015-09-30 | 深圳大学 | Microcapsule for self-repair concrete and preparation method of self-repair concrete |
| CN110698108A (en) * | 2019-12-02 | 2020-01-17 | 马鞍山十七冶工程科技有限责任公司 | Concrete self-repairing capsule and preparation method and application thereof |
| CN113045283A (en) * | 2021-03-24 | 2021-06-29 | 交通运输部公路科学研究所 | Intelligent trigger type concrete micro-crack self-repairing microcapsule and preparation method thereof |
-
2021
- 2021-11-24 CN CN202111407004.8A patent/CN114014602A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2015074343A1 (en) * | 2013-11-25 | 2015-05-28 | 深圳大学 | Microencapsulation method for concrete water-based repair agent |
| CN104944833A (en) * | 2015-03-31 | 2015-09-30 | 深圳大学 | Microcapsule for self-repair concrete and preparation method of self-repair concrete |
| CN110698108A (en) * | 2019-12-02 | 2020-01-17 | 马鞍山十七冶工程科技有限责任公司 | Concrete self-repairing capsule and preparation method and application thereof |
| CN113045283A (en) * | 2021-03-24 | 2021-06-29 | 交通运输部公路科学研究所 | Intelligent trigger type concrete micro-crack self-repairing microcapsule and preparation method thereof |
Non-Patent Citations (3)
| Title |
|---|
| 何欣等: "氧化石墨烯在水泥基材料中的应用研究综述", 《粉煤灰综合利用》 * |
| 林智扬等: "包裹硅酸钠的微胶囊自修复混凝土在不同修复剂下的修复性能", 《硅酸盐通报》 * |
| 鞠建英等: "《膨润土在工程中的开发与应用》", 31 March 2003, 中国建材工业出版社 * |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114477838A (en) * | 2022-02-21 | 2022-05-13 | 四川省建筑科学研究院有限公司 | Crack self-repairing material applied to concrete |
| CN115684279A (en) * | 2022-10-31 | 2023-02-03 | 江苏科技大学 | Quantitative test device and method for crack self-repairing effect of cement-based material |
| CN115684279B (en) * | 2022-10-31 | 2023-11-21 | 江苏科技大学 | Cement-based material crack self-repairing effect quantitative test device and method |
| CN116573913A (en) * | 2023-05-08 | 2023-08-11 | 浙江台州利伟节能建材有限公司 | Light plastering gypsum mortar and preparation method thereof |
| CN117362002A (en) * | 2023-12-04 | 2024-01-09 | 山东理工大学 | High-temperature phase-change heat-storage ceramic tile with solid waste as raw material and preparation method thereof |
| CN117362002B (en) * | 2023-12-04 | 2024-02-02 | 山东理工大学 | High-temperature phase-change heat-storage ceramic tile with solid waste as raw material and preparation method thereof |
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